Conventional wireless networks improve throughput by taking into consideration the characteristics of the transmission channel. Channel measurements are normally done off-line. A subsequent data analysis then determines an appropriate mathematical or statistical model that best fits the measured channel data. In conventional code division multiple access (CDMA) wireless systems (i.e., IS-95, IS-2000 and WCDMA), a pilot signal is transmitted continuously in the forward channel (or forward link) for the subscriber station to estimate the channel quality. The subscriber station then transmitted a received signal measurement value (e.g., RSSI) back to the wireless network. The measure signal data is then used to determine the necessary transmission power level or achievable data rate for the maximum transmission power.
Although a typical CDMA receiver also performs a similar search on the pilot signal for multipath components, the results of this operation are usually used for RAKE receiver implementation or pilot-weighted received signal combining. Unlike an orthogonal frequency division multiplexing (OFDM) system, a chief concern of a CDMA system regarding the delay spread is the detection and collection of energy from the multiple replicas of the transmitted data signal that arrive via various path components. In an OFDM system, the length of the guard interval or cyclic prefix is selected such that, when an OFDM symbol is transmitted, no significant amount of energy due to the channel delay spread interferes with the subsequent symbol.
Other algorithms for estimating channel parameters such as delay and magnitude of each multipath component or power delay profile are known to those of skill in the art. However, these techniques are mainly used to obtain channel measurement data that are subsequently used for off-line modeling and analysis of the channel characteristics. Other known techniques may require a design tradeoff selection of signal parameters which may not be easily changed after the system is deployed. The selected parameters may not be optimized for all the different deployment environments, nor when the channel environment changes, specifically, between the base station and the current group of users in its serving area.
In most conventional wireless systems (e.g., IEEE-802.16e and the IEEE-802.16-2004 standard, incorporated by reference), the transmit signal waveform parameters are selected when a cellular network is provisioned. The standard does not explicitly support the adaptability of changing the parameters as the channel characteristics change. On the other hand, conventional channel measurement methods are currently done to obtain data for the purpose of specifying the system design parameters. The measurements were not used as information to change signal waveform parameters in real-time.
Therefore, there is a need in the art for an improved wireless network that optimizes the forward channel signal waveform characteristics. In particular, there is a need for wireless network base stations that optimize the forward channel signal waveform characteristics according to changing forward channel conditions.